1. Field of the Invention
The present invention relates to a motor control device and a method for identifying, especially inertia in a control device such as, e.g., a robot and a working machine.
2. Description of Related Art
FIG. 3 shows a control structure of a conventional motor control device. The reference numeral 21 denotes a motor control unit, 22 denotes a model control unit, 23 denotes a velocity control proportional gain, 24 denotes a differentiator, 25 denotes an integrator, 26 is a velocity control proportional gain of the model control unit, 27 denotes an integrator showing the inertia of the model control unit, and 28 denotes an integrator. Vref denotes a velocity instruction, Vfb denotes a motor velocity, Tref denotes a torque instruction, STref denotes a torque instruction time integrated value, Vfb′ denotes a model velocity, and STref′ denotes a model torque instruction time integrated value. In a conventional motor control device, the motor control device is equipped with a motor control unit for controlling a motor velocity and a model control unit for simulating a velocity control by a model, and configured to identify the inertia based on the ratio of the value STref obtained by temporal integration of the torque instruction of the velocity control unit and the value STref′ obtained by temporal integration of the torque instruction of the model control unit when the motor is operated in accordance with a predetermined velocity pattern (see Patent Document 1).
Furthermore, the conventional motor control device is also equipped with a velocity instruction signal generation unit for generating a velocity pattern in which a control object is accelerated/decelerated in accordance with a predetermined pattern, a position control unit for controlling the position of the control object and a velocity control unit for controlling the velocity of the control object by accelerating/decelerating the control object based on the velocity pattern generated from the velocity instruction signal generation unit, and an observation device including an encoder for observing the current position of the control object.
In FIG. 4, Step 4-1 is a step of accelerating the load inertia up to an instruction velocity Vmax. Step 4-2 is a step of discriminating whether the instruction velocity V has reached a set instruction velocity Vn. The set instruction velocity Vn should be 50% or more of the maximum instruction velocity Vmax. The preferable set instruction velocity is about 70% thereof. Step 4-3 is a step of calculating the deviation at the time of Vn when the instruction velocity V has reached the set instruction velocity Vn. Step 4-4 is a step for discriminating whether the instruction velocity V has reached the maximum instruction velocity Vmax. Step 4-5 is a step for decelerating the actual velocity down to a stop (instruction velocity=0) when the instruction velocity V has reached the maximum instruction velocity Vmax. Step 4-6 is a step for discriminating whether the actual velocity has reached zero. Step 4-7 is a step for identifying the load inertia based on the deviation.
In accordance with the method shown in FIG. 4, the load inertia of the control object is identified based on the positional deviation between the instruction position of the control object and the current position observed by the observation device at the time when the instruction velocity generated from the velocity instruction signal generator has reached a previously set predetermined velocity (see Patent Document 2).
Patent Document 1: International Official Gazette No. WO96/37039 (page 6, FIG. 1)
Patent Document 2: Japanese Patent No. 3509413 (page 12, FIG. 5)
In a conventional control constant adjusting device for identifying inertia, the identification accuracy varies depending on a velocity instruction pattern shape. Accordingly, the velocity instruction pattern should be determined by trial and error. Since the predetermined velocity pattern determined as mentioned above is used, there is a problem that the identification operation cannot be executed depending on the limitations of the movable range, the velocity and the acceleration of the installed machine. Furthermore, in the examples disclosed in Patent Document 2, there is a problem that the prediction of the movement distance cannot be performed.